246 ■ CHAPTER 13 Adaptation and Species
with either of the two original parent species (the gray and the
Gambel), which of the following would you say most likely led to the
new hybrid species?Gray oakGambel
oakHybridsGray oak tree Gambel oak tree(a) prezygotic reproductive barriers(b) sympatric speciation(c) allopatric speciation(d) postzygotic reproductive barriers(e) none of the above(^11) The four-eyed fish, Anableps anableps, really has only two eyes,
which function as four, enabling the fish to see clearly through
both air and water. A. anableps is a surface feeder, so the ability
to see above water helps it locate prey such as insects. Its unique
eyes also enable it to scan simultaneously for predators attacking
from above (such as birds) or below (such as other fish). This
species of fish crafted by natural selection.
Anableps anableps
(a) is an example of coevolution
(b) has an evolutionary adaptation
(c) is an example of sympatric speciation
(d) is an example of allopatric speciation
(^12) Give an example of a barrier that might bring about allopatric
speciation. In addition to this barrier, what would be necessary for
speciation to occur?
(^5) Select the correct terms:
Speciation due to geographic separation and (genetic divergence /
gene flow) of two populations is considered (allopatric / sympatric)
speciation.
(^6) Select the correct phrases:
(Prezygotic barriers / Postzygotic barriers) are reproductive
isolating mechanisms that occur after a zygote has been formed. An
example would be (an infertile hybrid / gametes that cannot fuse).
Challenge Yourself
(^7) Natural selection
(a) leads to species being better adapted to their environment.
(b) may lead to speciation if there is no gene flow between
populations.
(c) may lead to genetic divergence among populations in differing
environments.
(d) all of the above
(e) none of the above
(^8) Which of the following examples describe an adaptive trait?
(Select all that apply.)
(a) A rainforest tree that is vulnerable to storm damage.
(b) A male bird that is more successful than others at attracting a
female mate.
(c) A rabbit that is better camouflaged in its environment.
(d) A desert plant that is able to survive drought.
(e) A frog that is more noticeable to predators.
(^9) Place the following events in the order in which they are most
likely to occur by numbering them from 1 to 5.
a. Speciation occurs.
b. Genetic divergence takes place.
c. Geographic barrier arises.
d. Gene flow is discontinued.
e. Species adapts to a new environment.
Tr y Something New
(^10) Distinct species that are able to interbreed in nature are said
to “hybridize,” and their offspring are called “hybrids.” The gray
oak and the Gambel oak can mate to produce fertile hybrids in
regions where they co-occur. However, the gene flow in nature
is sufficiently limited that, overall, the two species remain
phenotypically distinct. If the hybrid offspring survive well and
reproduce to the extent that there is a large population of hybrid
individuals that breed between themselves but do not interbreed